A wireless system for allocating a predetermined number of subcarriers as a plurality of resource blocks to terminals includes a base station that communicates with the terminals, wherein the base station sets m resource blocks adjacent to one another in a frequency domain as a resource block group, m being a positive integer, and uses a first communication method and a second communication method, the first communication method repeatedly and sequentially classifying the resource block group into m kinds of subsets from a first subset to an m-th subset, and the second communication method allocating two resource blocks, which are separated by a predetermined distance in the frequency domain, to a same terminal, wherein the predetermined distance being an integer multiple of m times m.
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1. A base station in a communication system where a predetermined number of subcarriers are allocated to a terminal as a plurality of resource blocks, and m resource blocks adjacent to one another in a frequency domain are set as a resource block group, m being a positive integer,
wherein the base station uses a first communication method and a second communication method,
in the first communication method, the resource block group being classified repeatedly and sequentially into m kinds of subsets from a first subset to an m-th subset, and
in the second communication method two resource blocks, which are separated by a predetermined distance in the frequency domain, being allocated to a same terminal, the predetermined distance being an integer multiple of m times m.
2. The base station according to
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The present application is a divisional of U.S. application Ser. No. 12/663,421, filed on Dec. 7, 2009, which was the National Stage of International Application No. PCT/JP2007/075181, filed on Dec. 27, 2007, which claimed priority to Japanese Application No. 2007-160698, filed on Jun. 18, 2007. Application Ser. No. 12/663,421 is hereby incorporated by reference in its entirety.
The present invention relates to a communication method, wireless communication system, and transmitter and receiver that configure the system when Localized transmission and Distributed transmission are mixed in the same sub-frame.
Currently in 3GPP, under the name of LTE (Long Term Evolution), a wireless system adopting a new wireless technique has been studied. In this wireless system, a plurality of data channel resources are defined on a frequency axis to measure the state of quality of each channel and, based on the measurement results, a data channel resource for use in communication is determined. And, a notification about the data channel resource determined therein is made as allocation information by using a control channel to each terminal configuring the system mentioned above.
Also, in a downstream (base station→terminal) frame studied as LTE, a control channel and a data channel are disposed in one sub-frame, and resource allocation is performed in units of this sub-frame. Further, in a system frequency band, 100 channels are present according to current studies. And, each of these channels is called a resource block, and is configured of, for example, twelve sub-carriers. Still further, to each terminal configuring the system mentioned above, one or a plurality of resource blocks can be allocated.
Still further, in LTE, a terminal regularly measures channel quality in units of one resource block or several resource blocks, and reports the measurement result to a base station in which a scheduler is present. Then, based on the report, the scheduler allocates a resource block of good quality to a terminal that performs channel allocation. In this manner, in LTE, a technique of data transmission with resource-block allocation based on the channel quality is referred to as “Localized transmission”. In this Localized transmission, in notifying a terminal of allocation information, a bit map is used, for example. When a bit map is used, N resource blocks present in a system frequency band are associated with N bits, and a bit corresponding to a resource block to which a terminal is allocated is set at “1”. For example, when eight resource blocks are assumed, with a terminal A having allocated thereto resource blocks #0, #1, #6, and #7, a terminal B having allocated thereto resource blocks #2 and #3, and a terminal C having allocated thereto resource blocks #4 and #5, allocation information for notification by using control channels are “11000011”, “00110000”, and “00001100”.
However, as explained above, since 100 resource blocks are present at maximum in LTE, notification to each terminal by using a bit map of 100 bits leads to a shortage of control channels. To avoid this shortage, in 3GPP, a method of regarding two resource blocks as one scheduling unit (hereinafter referred to as aggregation) has also been studied. For example, when the number of aggregation is assumed to be 2 and the allocation information mentioned above is represented with a bit map, pieces of the allocation information for notification to the terminal A, B, and C are “1001”, “0100”, and “0010”, respectively. Note that while this method is in a studying stage in 3GPP, aggregation of three or four resource blocks has also been studied as a technique of reducing the control channels.
On the other hand, although the Localized transmission mentioned above is an effective technique when the traveling speed of the terminal is slow, it cannot be much an effective technique when the traveling speed is fast. For example, since reporting the channel quality and scheduling require a certain processing time, when the traveling speed is fast, changes of the channel quality in a direction of time is quickened, and therefore the contents of the report of the channel quality may possibly be obsolete at the time of actual data transmission. In such circumstances, since the possibility of allocating a resource block with deteriorated quality and the possibility of applying an unsuitable modulation technique or the like are increased, it is not preferable to select a resource block based on the channel quality of individual resource blocks and further adaptively change a modulation technique and an error correction coding rate. Therefore, to a terminal with a fast traveling speed, a technique is taken in which data to be transmitted by that terminal is distributed into a plurality of resource blocks with a small correlation each other as to the channel state on a frequency axis. That is, a technique is adopted such that an average value of the channel quality of the allocated resource blocks is stabilized (frequency diversity). And, when this technique is adopted, the modulation technique and the error correcting coding rate are determined not based on the channel quality of individual resource blocks but based on the average channel quality of the entire system frequency. In this manner, a technique of data transmission by allocating resource blocks distributed on the frequency axis to the same terminal is referred to as “Distributed transmission”.
While general outlines of Localized transmission and Distributed transmission have been explained above, a specific method of making a notification about the resource blocks allocated by the respective techniques is explained next. In a first non-patent document mentioned below, a method of making a notification about allocated resource blocks regarding the respective techniques is disclosed.
Also, in a second non-patent document, “Sub-sampling transmission” is disclosed as a modification of the Localized transmission explained above. This Sub-sampling transmission is a method defined for allocating the remaining resources in units of one resource block after allocation of resource blocks with Localized transmission. Note that while the Localized transmission mentioned above and Sub-sampling transmission are both classified as Localized transmission and distinguished therein as approach 1 and approach 3, respectively, in 3GPP, they are distinguished hereinafter also as Localized transmission and Sub-sampling transmission for convenience.
In the studies in LTE of 3GPP explained above, Localized transmission and Distributed transmission are mixed in the same sub-frame. Also, the number of resource blocks for use in Distributed transmission is changed for each sub-frame or for every several sub-frames. In such circumstances, when the notifying method explained above is applied, problems as explained below will occur.
Also, in
When
Furthermore, in LTE of 3GPP explained above, there is no statement at all about definitions regarding to which resource block each bit of the bit map corresponds when Localized transmission and Distributed transmission are mixed in the same sub-frame.
When Sub-sampling transmission is mixed in the same sub-frame in addition to Localized transmission and Distributed transmission, a problem as depicted in
The present invention has been devised in view of the above, and an object thereof is to obtain a communication method capable of avoiding complexity of a receiving process when Localized transmission and Distributed transmission are mixed in the same sub-frame.
The present invention has been devised in view of the above. An object thereof is to obtain a communication method that enhances flexibility in allocating resources for Sub-sampling transmission when Localized transmission, Distributed transmission, and Sub-sampling transmission are mixed in the same sub-frame.
To solve the abovementioned problem, and to achieve the above object, a wireless system for allocating a predetermined number of subcarriers as a plurality of resource blocks to terminals includes a base station that communicates with the terminals, wherein the base station sets M resource blocks adjacent to one another in a frequency domain as a resource block group, M being a positive integer, and uses a first communication method and a second communication method, the first communication method repeatedly and sequentially classifying the resource block group into M kinds of subsets from a first subset to an M-th subset, and the second communication method allocating two resource blocks, which are separated by a predetermined distance in the frequency domain, to a same terminal, wherein the predetermined distance being an integer multiple of M times M.
To solve the above mentioned problem, and to achieve the above object, in a wireless communication system where data transmission is performed between a base station and terminals by using a system frequency band configured of a plurality of resource blocks, a communication method according to one aspect of the present invention when two transmission types, Localized transmission and Distributed transmission, are mixed in a same sub-frame, includes, as a process to be performed by the base station, a transmission-type selecting step of selecting a transmission type to be applied to each terminal, based on traveling speed information obtained from each of the terminals configuring the wireless communication system; a number-of-aggregation determining step of determining the number of aggregation based on the number of terminals to which Localized transmission is applied; a bit-map generating step of individually generating, for each terminal, a bit map indicative of scheduling resource numbers to be allocated to the terminals to which Localized transmission is applied, based on a resource-number mapping rule defined by individually providing resource block numbers to all of the resource blocks, taking resource block numbers of resource blocks for Distributed transmission as fixed values, and individually providing scheduling resource numbers to remaining resource blocks for Localized transmission except the resource blocks for Distributed transmission for each of scheduling resources corresponding to the number of aggregation; and an allocation-information generating and transmitting step of generating and transmitting, for each terminal, resource allocation information including the transmission types and the bit maps.
Furthermore, in a wireless communication system where data transmission is performed between a base station and terminals by using a system frequency band configured of a plurality of resource blocks, a communication method according to another aspect of the present invention when three transmission types, Localized transmission, Distributed transmission, and Sub-sampling transmission, are mixed in a same sub-frame, includes, as a process to be performed by the base station, a transmission-type selecting step of selecting a transmission type to be applied to each terminal, based on traveling speed information obtained from each of the terminals configuring the wireless communication system; a number-of-aggregation determining step of determining the number of aggregation based on the number of terminals to which Localized transmission is applied; a resource-block-for-Sub-sampling-transmission selecting step of selecting, as resource blocks to be allocated for Distributed transmission, based on the determined number of aggregation, resource blocks belonging to a specific single subset among a plurality of subsets for use in Sub-sampling transmission; a resource-block allocating step of allocating resource blocks to each terminal based on the determined number of aggregation and the selection result at the resource-block-for-Sub-sampling-transmission selecting step; and an allocation-information generating and transmitting step of individually generating and transmitting, for each terminal, resource allocation information including the transmission types and the allocation result at the resource-block allocating step.
According to the present invention, an effect can be achieved such that, even in a system where Localized transmission and Distributed transmission are mixed in the same sub-frame, the receiving process by the terminal can be simplified, compared with the conventional technology, and an increase in circuit size and process delay can be avoided.
According to the present invention, an effect can be achieved such that, even in a system where Localized transmission, Distributed transmission, and Sub-sampling transmission are mixed in the same sub-frame, flexibility in allocating resource blocks for Sub-sampling transmission can be enhanced, compared with the conventional technology.
In the following, embodiments of the communication method, wireless communication system, and transmitter and receiver that configure the system according to the present invention are explained in detail based on the drawings. Note that the present invention is not meant to be restricted by these embodiments.
In the base station depicted in
On the other hand, in the terminal depicted in
Here, prior to explanation of features of the present invention, the technology on which the present invention is predicated is explained.
And,
However, as explained above, since 100 resource blocks are present at maximum in LTE, notification to each terminal by using a bit map of 100 bits leads to a shortage of control channels. To avoid this shortage, in 3GPP, aggregation has also been studied. When aggregation is performed to represent the allocation depicted in the example of
On the other hand, it has already been explained that, although the Localized transmission mentioned above is an effective technique when the traveling speed of the terminal is slow, it cannot be much an effective technique when the traveling speed is fast.
And,
Next, in consideration of the technology explained above on which the present invention is predicated, a resource-allocation notifying method of the present embodiment is explained.
First, in the present embodiment, the scheduler 2 determines in advance a maximum value of the number of resource blocks for use in Distributed transmission and its position, and these pieces of information are shared between the base station and the terminals. Then, with that position being excluded, the scheduler 2 defines a method of providing a unique scheduling resource number for each number of aggregation. Specifically, in
With the mapping rule mentioned above being shared, based on the traveling speed information obtained from each terminal, the scheduler 2 of the base station generates information regarding the transmission type to be included in resource allocation information of which each terminal is notified. That is, whether Localized transmission is applied or Distributed transmission is applied is selected. Also, based on the channel quality information obtained from each terminal, a terminal to perform data transmission is selected, and a modulating technique and others are selected. Furthermore, based on the number of terminals for scheduling (terminals to which Localized transmission is applied) and others, the number of aggregation at the time of Localized transmission is determined. Based on this number of aggregation, a bit map for making a notification about a scheduling resource number indicative of a resource block to be allocated to the terminal to which Localized transmission is applied is generated individually for each terminal. Then, resource allocation information including these pieces of information is generated for each terminal, and each terminal is notified of this information.
In this manner, in the present embodiment, the positions of the resource blocks for Distributed transmission are defined in advance and, with these being excluded, scheduling resource numbers for Localized transmission are defined. With this, in the terminal to which Localized transmission is applied, based on the mapping rule explained above, a correspondence between the resource block numbers for Localized transmission and the scheduling resource numbers can be uniquely recognized for each number of aggregation. Therefore, irrespectively of the number of resource blocks for use in Distributed transmission, resource blocks allocated to its own station can be specified only with a resource allocation notification with a bit map. That is, the scheduler of the base station is not required to notify the terminal to which Localized transmission is applied of N_DPRB. Therefore, according to the present embodiment, even in a system where Localized transmission and Distributed transmission are mixed in the same sub-frame, a receiving process by the terminal can be simplified, compared with the conventional technology, and an increase in circuit size and process delay can be avoided.
Note in the above that, for the purpose of simplifying explanation, explanation has been made based on the premises that resource blocks allocated for Distributed transmission are not used as for Localized transmission (refer to
Subsequently, a communication method different from that in the first embodiment explained above is explained. Note that the structures of the base station and the terminals are similar to those in the first embodiment explained above. Here, processes different from those in the first embodiment are explained.
Note in the above that while the resource blocks for Distributed transmission can be used also for Localized transmission, this is not meant to be restrictive and, for example, as depicted in
In this manner, in the present embodiment, scheduling resource numbers are provided as depicted in
This is very effective in view of retransmission of transmitting data with the same data size as that of initial transmission, when flexibility occurs in the scheduler and the channel quality state is changed at an initial transmission timing and a retransmission timing.
Also, in
Note that
Also, in the present embodiment, as depicted in
For example, without providing scheduling resource numbers to individual resource blocks for Distributed transmission, an indicator of one bit can be set to the bit map for each terminal. When this indicator indicates “1”, each terminal recognizes such that, for example, resource blocks for Distributed transmission that are present at the right of the resource blocks allocated to itself in Localized transmission and resource blocks for Distributed transmission interposed between resource blocks allocated to itself in Localized transmission are all allocated to itself.
Subsequently, a communication method different from those in the first embodiment and the second embodiment explained above is explained. Note that the structures of the base station and the terminals are similar to those in the first embodiment explained above. Here, processes different from those in the first and second embodiments are explained.
As can be seen in comparison with
When a process of providing scheduling resource numbers depicted in
Note in the present embodiment that explanation has been made based on the premise that resource blocks allocated for Distributed transmission are definitely used as those for Distributed transmission. However, for example, by using the concept of an indicator explained above, resource blocks allocated for Distributed transmission can be used as those for Localized transmission. For example, when the indicator indicates “0”, the terminal specifies, through the process explained above, all resource blocks for Localized transmission allocated to itself other than the resource blocks for Distributed transmission. On the other hand, when the indicator indicates “1”, even when a resource block allocated to itself with a bit map and a resource block allocated for Distributed transmission overlap each other, the terminal determines that these resource blocks are allocated to itself for Localized transmission, and performs a demodulating and decoding process on all resource blocks allocated to itself with the bit map. By performing this process, the resource blocks allocated for Distributed transmission can be used for Localized transmission, thereby providing flexibility to the scheduler.
In the first to third embodiments explained above, the communication method when two transmission types, Localized transmission and Distributed transmission, are mixed has been explained. Next, a communication method when Sub-sampling transmission is further mixed in addition to these Localized transmission and Distributed transmission is explained. Note that the structures of the base station and the terminals are similar to those in the first embodiment explained above. In the present embodiment, processes different from those in the first to third embodiments are explained.
Note that, as long as the condition “resource blocks for Distributed transmission belong to the same subset” is satisfied, resources may be allocated first to whichever terminal in the scheduling (resource allocation), either of a terminal to perform Distributed transmission and a terminal to perform Localized transmission. That is, it does not matter which scheduling is to be performed first, scheduling for a terminal to which Distributed transmission is applied or scheduling for a terminal to which Localized transmission is applied.
With this, when allocation is performed later in Sub-sampling transmission, since Part A and Part B of the remaining resource blocks belong to the same subset, these can be allocated to the same terminal. Also, as with the conventional technique, the possibility of allocating these to different terminals is still kept. That is, flexibility when resources for Sub-sampling transmission are allocated can be increased. Meanwhile, although a plurality of values that satisfy the condition mentioned above are present as a distance N of the resource blocks on the frequency axis for use in distributed allocation, the value can be fixed to one value for simplification of processes in the system and a receiver. In this case, it is assumed that N is an integral multiple of M×M. As mentioned above, M represents the number of aggregation for Localized transmission, and is also the number of subsets at the time of Sub-sampling transmission.
Also, when the number of distribution for Distributed transmission is 2, 3GPP has already stipulated that data is divided into two and the first half portion and the latter half portion of the data are mapped to different resource blocks (refer to
Note that, as with the case of the first to third embodiments explained above, the scheduling results obtained by the scheduler 2 are transmitted by the encoding/modulating/transmitting unit 3 to each terminal as resource allocation information. The resource allocation information transmitted from the base station to each terminal in the present embodiment includes information about the transmission type, a bit map representing the results of resource allocation to Localized transmission or Sub-sampling transmission, information indicative of the results of resource allocation to Distributed transmission (for example, indexes of resource blocks where the first half portion of data when the number of distribution in Distributed transmission is 2 is mapped), and others.
As for the first to fourth embodiments explained above, the following coordination or randomization technique can be applied. For example, in a cellular system where a plurality of base stations are disposed as a plain, the same system frequency band is repeatedly used. That is, the same frequency band and the same resource block may be used between adjacent base stations. In this system, a resource block allocated to a specific terminal is used in the area of an adjacent base station, and this may always cause interference. To avoid this, coordination or randomization is performed. For example, coordination is a technique of avoiding mutual interference by shifting resource blocks for Distributed transmission between adjacent base stations. And, randomization is a technique in which the interval of the resource blocks for Distributed transmission is not made constant, to create a situation in which specific resource blocks collide with each other between adjacent base stations but other resource blocks do not collide with each other.
In LTE, a technique is handled in which, when transmitted data cannot be correctly received at a receiving station, the same data is retransmitted. While N_DPRB can be varied in the above, a restriction may be provided in consideration of retransmission. That is, the restriction is such that N_DPRB at a retransmission timing has the same value as that of N_DPRB at the previous transmission timing. With this restriction imposed, the number of resource blocks becomes the same between Localized transmission and Distributed transmission and the position of the resource block becomes the same between the previous transmission timing and the retransmission timing. At the retransmission timing of retransmitting the same data, resources can be advantageously secured with ease.
As has been explained in the foregoing, the communication method according to the present invention is useful as a resource-allocation notifying method when, from among Localized transmission, Distributed transmission, and Sub-sampling transmission, at least Localized transmission and Distributed transmission are mixed in the same sub-frame.
Fukui, Noriyuki, Tani, Shigenori
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